Theoretical physics

since the thread about about free will arised some questions about physics people asked me about physics. Usual people do not know very much about physics, but one cannot blame them, but the educational system and teachers (IF you want to blame someone, since people can have a nice live without knowing anything about physics, so there might be no need to know physics). Some also asked me to make a thread in which people could ask question about physics. So why not, here it is, ask any questions about physics you always wondered (preferable in theoretical physics, since experimental physics is so huge, that it is very unlikely I will be able to answer specific questions).

Teleportation. Go.

@Mechazawa: Ok, let me first define two types of teleportation how I think what you mean (if you mean something else, please tell):
1.: the teleportation of matter like in doom.
I do not see why this should not be possible, you have to somehow get the "complete" (<- not possible, but up to 99.9999999%) information of the system you want to teleport. Then simply transport this information e.g. with wires to the destination point and reconstruct the system with the information and a pool of atoms (3D printer with atoms if you like). This would be a teleportation with a very high sprecision (not 100% but it should be enough for everything we want to teleport). Teleportation with a low precision in that sence I would say is for example fax machines.

2.: the instantaneous teleportation of matter like in doom.
if this is possible, then, you can transport information in an ordinary (without any shortcuts) space faster than the speed of light. This is prohibited by Einstein.
Why do we believe in Einstein?
First there is no observation of superluminal information in ordinary space, e.g. we can accelerate protons at LHC very close to the speed of light, but they do not exceed it. What nature shows us, that the particles and forces we can observe are slower or as fast as the speed of light. Apart from that, there are many superluminal aspects in nature, but none of them transfer information.
Secondly by restricting to operate with velocities v smaller than c, one can conclude a lot of aspects of nature, which all can be measured in experiments.
-> There is no need to claim Einstein is wrong.
Ok, too bad, no superluminal transportation... what about shortcuts then? In Einsteins general relativity shortcuts also called wormholes are allowed (For example in the presence of a black hole, although then you cannot teleport to another place in our universe, but to a different place in a different universe). Although this might be doable, when we think about such stuff, we extrapolate the theory of Einstein to reagions, which are not reachable with experiments (at least not yet). And this is kind of dangereous. For example if you had asked Newton if teleportation is doable he would have said yes, why not? Because if you take only Newtonian Mechanics, there is no boundary for the velocities of bodies (actually to Newtons time there were people believing that the speed of light is not infinite, but I am not sure Newton was aware of this, nevertheless I am not speaking of history, but about the models). So the point I want to make is, that it might be possible, there is no better theory which prohibits it yet, but it is highy questionable if one can use general relativity in such circumstances (not only because of this problem, there are more).

If you want to know something more about it, or specific parts, just tell me.

Further I want to say, what I am answering is what our currently best models of nature we have tells us. Physics cannot say that teleportation is not doable in general, but our current models of it can. If the models are right or not, we can only argue right now, since we have no experiments which say us so.

What are your thoughts on the possibility of a resonance cascade?

Parallel universes and how many Ashstrodamus's are there within said universes?

@Piper Maru: After a quick google search I am quite sure you are talking about Half Life (although I played it a lot, I had no idea about the plot, since I could not understand english when I played it in single player). I could not find a lot of information about the process, but as far as I have seen, it somehow produces energy out of nowhere. Further something like wormholes appear. Well if you can produce a large amount of energy wormholes might appear (see first answer in this thread). But how can this energy produced out of nowhere? Resonances appear by applying the energy from outside, but the resonance does not produce it and also fade away if the energy source is capped. If you take the energy from outside, then there will not be enough on earth to do it, so no I do not think it is possible. If you can tell me more specific what it is and what I might miss, feel free to tell me.

@Ashstrodamus: First I also wanted to google what Ashstrodamus is ;). Well parallel universes is a nice concept in philosophy. Why philosophy and not physics? Because there are no experiments to test anything about them. A famouse case for parallel universes is the many world theory as an interpretation of quantum mechanics. If you make a measurement our universe gets copied and any possible outcome will come out in one universe of the copied ones. If this is true, then there would be universes in which each experiment made a classical output and not a quantum output. The sad people in these universes would think that their classical model of nature would be complete..., very sad consequence. To approximate how many Ashstrodamus are in the universes, one have to know in how many you would have been born and how often they got copied. In chaos theory, if you change a small value at the beginning, after a short time the system varies completely compared to the original one iwthout the small change. So I would say, there is only a very small friction of universes in which you (or something very similar to you) have been born. Since your age is also very small compared to the age of the universe, the amount of copied universes in which you already live is also tiny. Although the friction might be very small, the total number of universes with a Ashstrodamus would still be enormous large (bigger than for example the number of protons in our observed universe).
Apart from many world theory, one can also think of other universes which were not copied from our universe, but are simply other universes, maybe and maybe not connected with ours (for example like bubbles on a foam). This could explain why our nature is so damn good balanced. For example if you vary any natural constant a bit, our universe how we know it would not exist and therefore we would not also... So since it is very unprobable the nature could be like this and inhabitable by us, it is nice to think there are A LOT of other universes which we could not inhabite. If you have such a high number, there might be some which can form stars, planets and even creatures which can think of the universe (the universe thinks about itself :)).

@antares031: true, there is even scientific work about such concepts... but as I said in the first my first answer, it is dangerouse to extrapolate theories in regions where we have no experiments. If you look up the scientific work, you will find that it changed fundamental concepts of nature (negative mass). Einstein's theory has no problem with that and warp drive follows, but negative mass has never been observed. It might be true that it is possible, but as you said even if it is, there is no way how mankind can bring up such amount of negative energy. Also matter antimatter would not solve this problem, since it only produced energy, and it also only changes you mass into energy which gives you zero effect on the spacetime.

Can you describe water? And birds?

@Gez: No, could you do?

They are sassy.

Ok, one question
How does SCP-914 function?
scp-wiki.net/scp-914/

That's not so much theoretical physics as it is Sailor Moon magic.

@Voros: read the important parts of the site, no idea sorry, but does it even have to work in our world? As you said on your blod you can write anything on this site.

@Jaxxoon R: if this is the case, then no idea :), I am not familiar with Sailor Moon magic or any kind of other magic

@antares031: You are welcome, I am glad I could help for better understanding. I know there are websites and news papers who just claim that there is warp drive and even refer to the scientific word, but never say a word about what the underlying changes of our nature is..., that is bad in my opinion (but of course easier for the journalist, than to read the work for himself).

Eh, just wanted to see if its possible to explain 914.

My real question: What exactly is "dimensions"? Is there a 4th dimension? Is it even possible?

Side question: Will we ever find the next earth? If so, would it possibly be like a rocky giant with boiling temperatures? Like all the others discovered? Is it possible to reach such a place, which is many lightyears away in the most efficient way possible?
Yes, I saw a Nat Geo special called "Finding the Next Earth"

What does physics tell us about dimensions? It depends what theories you are using, for example for Newton, there were 3 spatial dimensions in which objects are placed. Space consists of nothing and can be only "seen" as the distance between objects one can see. For Einstein the distance between these object even depends on their velocities and what is also new for Newton, on the observer's velocity. Together with the limit of the speed of light you can conclude that space and time are connected and you cannot describe one without the other. Therefore there is not space and time anymore, but spacetime. This is why the 4th dimension is the time. Your question about the 4th dimension may have been about a 4th spatial dimension. Well as you and me can see, in our daily life there are only 3 spatial dimensions, length, heith and depth. So if there are more spatial dimensions (and there are theories which need them, e. g. string theory), then they are very small and only reachable with energies we are not able to reach (yet). Yes it is possible, in such theories of course different laws of physics are concerned, but good ones have as a limit our known laws in 4D.

Depending on what you mean with next earth, we will for sure find planets on which humans could live on. Why? Well the material our earth is made of comes from clouds of star dust. These are very common in our milkyway and therefore solid planets are also not rare at all. Further the distance to it's star has to be in the habitable zone (not too cold, not too hot, water has to be near liquid). And of course water. All parameters together are unlikely to be on a planet, but as we discover more and more planets, there will be one for sure with good parameters.

Ok to reach it is a different problem, of course the farther away we have to search for such a good planet, the longer it would take to reach it. Such a nice planet might not be in our closest neighborhood. You can call me a dreamer, but I think if mankind manages to live for the next thousand of years, travels to other stars (at least the closest ones) are doable. Compared to the energy needed for other projects discussed earlier, the energy needed for such a jurney is nothing and doable with the energy resources in our solar system. Will this happen in our lifetime? Of course not. Even if a rocket would start tomorrow with for example a huge matter antimatter tank, we would not see the astronauts reaching the next star (Fun fact: if you were one of the astronauts you might get there in your lifetime, but because of time dilatation on earth the time went faster w.r.t. you, so you cannot tell your children, or grand-grand-grand... children of your discovery).

Will future AI go rogue somehow due to complexity of their system. Nothing like the Terminator or Ultron, but something like a petty crime, like hacking into the bank system instead of protecting it.

Is this a question about physics? In physics there is no problem with that. Further I cannot think of an argument why such things should not be possible with system with ongoing complexity.

I guess not.

Isn't there a better way to produce electricity as much as possible, with 60-90% efficiancy?
I know rotating magnets/iron core with coils of wires are involved.
Anyway to make safely produced electricity that works immensely well, like nuclear power without the radioactivity?

Actually I am not an expert in electricity (as I said in the first post, experimental physics is huge), I do not know which technology you mean which produces electricity with such a high efficiency.
With nuclear power you for sure mean nuclear fission with byproducts which are radioactive. Well there is nuclear fusion, a huge amount of the energy on earth is because of it. Sadly the fusion core is 150 000 000 km away. But scientists are trying to build fusion reactors on earth too.
There are three main concepts:
-shoot a solid sphere with huge lasers which makes the shell of the sphere to explode. The repulsion of the explosion makes the core of the sphere very very dense such that nuclear fusion appears. The best facility for that is NIF (US facility, so also used for military purposes): https://en.wikipedia.org/wiki/National_Ignition_Facility
-enclose plasma with a magnetic field and heat it such that fusion takes place. A huge project is planned for europe ITER:
https://en.wikipedia.org/wiki/ITER
-put 10^30 kg of hydrogen onto a spot and let gravitational attraction do the rest. Already done in the center of our solar system.

With nuclear fusion the amount of radioactive material is a small fraction of that of nuclear fission and more importantly, the elements produced have a life time in the range of decades... and not 100000 years.

Isn't radioactive decay triggered during nuclear fission, with the atom changing it self into two or more elements? How does that really work?

Radioactive decay isn't triggered by anything in particular. It's more accurate to say that radioactive decay triggers fission than to say that fission triggers radioactive decay. I recommend reading these thee articles in sequence: Energy levels, chains of decay, working to fusion. I find them well-written and entertaining.

@Hellbent: as Gez said, the temperature does not have to be as big as the melting point, a lower temperature can be sufficient. One thing you should not forget is the high pressure from the floors above. But I think this is a better question for a structural engineer, he might can tell you how much pressure those steel girders can sustain. Together with an material specialist who can say you how the sustainability decreases with incresing temperature, one can find a good answer to that question for sure. Since you and me do not know such experts, we can only believe what the officials say or not. But if it is so unlikely that there had to be explosions, then I think there would be other countries claiming exactly this. But afaik there are only voices from a few people.

@Voros: You may think of fluids (one of the first models for nuclei were really fluid mechanics, which can explain a lot for that it shares only a few concepts with nuclei):
You have a waterdrop levitating in our lab which is for example in the ISS (0 gravity). A small drop is stable as it is, floats around, nothing happens. Now you inject more and more water to the drop and make it bigger and bigger. If you reach a critical size the drop will eventually split into smaller drops. In general, the bigger the more likely it will split. This you can think of an analogy to radioactive decay. The analogy to nuclear fission would be you take a big waterdrop which would maybe split in a few years, so not very radioactive. But now you shoot the big drop with a small drop which will trigger the split into medium drops and also into small drops. These small drops will again hit other big drops and you will have a chain reaction if all conditions are good for it (e.g. density of big drops). The radioactive waste are the medium drops, they are big enough to decay.

termrork said:

@Hellbent:

Why don't I see Hellbent anywhere in this thread?

By reading the answer, we can probably guess what the question was, and hence why :P

actually, there was a question and also an answer by gez to that question.
I wonder why my answer was not deleated.

I think I saw this on TV. I'm no physicist, it may be do with string theory, I'll try to remember...

Something to do with subatomic particles sharing information states when they were created? And if something changes to one, the other must also change, regardless of where it is in the universe?

So quantum information is possibly innate to the universe and information in the universe can therefore presumably travel faster than light?

Nono you do not need string theory for this, you can do this in any quantum theory. What you are describing is entanglement. For example you can create two entangled photons (quantum of light) and as you say, you can measure properties of one photon and instantaneously know what these properties from the other photon are, no matter how far it is away. So can you transport information instantanously? No since when you measure particle A, YOU know all the information about B, not the guy who receives particle B. Since the output of the measurement is random, you cannot communicate with this setup. If you could force the particle to be measured to give value a, then you know the other particle will give b and you could transfer information via morse, but this is not possible.
Btw, this is no theoretical concept, there are a lot of laps using entanglement and experiment with it.

Eris Falling said:

By reading the answer, we can probably guess what the question was, and hence why :P

I'm almost surprised it was completely nuked, then again I'm not surprised. I will say no more.

I have another physics question. Well, really it's a math problem.

This one involves aerodynamics and wind resistance. If an airliner has a maximum speed of 535mph at 35,000 feet, what is its maximum speed at sea level? The density of the atmosphere is more than 3 times thinner at 35,000 feet. (Something like 30% of the density at sealevel). Given that the limiting factor for an airliner at 35,000 feet to travel at 535mph is wind resistance, we have to assume the max speed will be much slower at sea level, where wind resistance is much greater, but what is it? Thanks!

Hellbent said:

This one involves aerodynamics and wind resistance. If an airliner has a maximum speed of 535mph at 35,000 feet, what is its maximum speed at sea level? The density of the atmosphere is more than 3 times thinner at 35,000 feet. (Something like 30% of the density at sealevel). Given that the limiting factor for an airliner at 35,000 feet to travel at 535mph is wind resistance, we have to assume the max speed will be much slower at sea level, where wind resistance is much greater, but what is it? Thanks!

I'm gonna go ahead and say that this is entirely determined by the specific propulsion system the aircraft utilizes moreso than its aerodynamic qualities. A sedan could travel at mach 3 with the proper engines I suppose.

I remember my 10th grade science teacher said that pretty much every physist believed in extraterrestrial life to some degree, so what are your thoughts on this?